Dune II: The Building of a Dynasty

While Dune II: The Building of a Dynasty wasn't technically the first real-time strategy game, it established the model that nearly all RTS games have followed ever since. In addition to managing a variety of units, players had to harvest resources, build massive bases (complete with a technology tree), and pretty much do everything else that we've come to expect from the genre. Dune II also benefited from some great production values, with fabulous music and an in-game helper (called a Mentat) who explained many of the concepts needed to win. Though it only had the slightest connection to the Dune novels, it was a great game the paved the way for all other RTS games to come.